1. Field of the Invention
The present invention relates to a coil assembly for an electrical rotating machine, a stator for an electrical rotating machine, and an electrical rotating machine, and more particularly, a coil assembly and a stator for an axial type electrical rotating machine, and the axial type electrical rotating machine.
2. Description of the Related Art
In general, because coreless type electrical rotating machines (electric motors and electric generators) have no iron-based core member, in which magnetic saturation is caused by a coil current, in a coil member, the linearity of torque can be maintained relative to a large current, and it is possible to obtain a high instant maximum torque which is about five to ten times as much as a continuous rating torque.
Accordingly, the coreless type electrical rotating machines are used for adjustable-speed drives for a servo application or the like.
In order to achieve a high torque in the coreless type electrical rotating machines, it is necessary to increase a conductor thickness to allow a large current to flow therethrough, but the conductor thickness at a coil member directly affects a magnetic air gap, so that the magnetic air gap increases. Therefore, the magnetic resistance becomes large and the flux quantity decreases, resulting in reduction of an output power.
In the coreless type electrical rotating machines, due to the characteristic thereof, the magnetic flux directly interlinks a conductor, so that an eddy current is generated in the conductor. The eddy current causes a conductor-eddy-current loss. Conversely, if the width dimension of a coil facing a magnet is narrowed to suppress the conductor-eddy-current loss, the coil must have thinner lines, so that there is a contradictory problem that it becomes difficult to allow a large current to flow through. Further, thinning of the coil pattern (wiring pattern) results in decrement of the strength, and it becomes difficult to stably maintain the coil shape.
Therefore, according to the conventional coreless type electrical rotating machines, even though they have a high instant torque, their application is limited to small motors having a small output from several ten to several hundred Watts because of the foregoing reasons.
In particular, a stator coil for a small flat motor is formed with a pattern coil for thinning and miniaturization (see, for example, U.S. Pat. No. 6,411,002, FIG. 18), but if the pattern coil is used as a stator coil for a motor having a large output greater than or equal to, for example, several 10 k Watts, it is difficult to allow a large current to flow through because reduction of a conductor resistance is difficult, so that sufficient improvement of the output cannot be achieved.
Further, motors allowing a large current to flow for a large output application may have a cooling pipe closely contacted to the surface of a coil in order to efficiently cool down the coil (see, JP 2001-25211 A).